Exhaust gas turbocharger for an internal combustion engine

ABSTRACT

An exhaust gas turbocharger for an internal combustion engine comprises a turbine in the exhaust line and a compressor, which is driven by the turbine and which is located inside the intake tract of the internal combustion engine. The turbine comprises a flow duct having a radial flow entrance cross-section, and a flow ring is provided that delimits the flow entrance cross-section. An adjustable vane is placed in the radial flow entrance cross-section for variably adjusting this flow entrance cross-section. The flow ring inside the housing of the exhaust gas turbine can be axially displaced between a contact position toward the vane and a position that frees a gap toward the vane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns an exhaust gas turbocharger for an internalcombustion engine according to the precharacterizing portion of claim 1.

2. Related Art of the Invention

From the publication DE 196 15 237 C2 an exhaust gas turbocharger ofthis general type is known, having a turbine with a radial and asemi-axial flow intake cross-section in the exhaust flow area of theturbine. The flow intake profiles, between which a flow promotingcontoured flow ring is provided in the flow intake area of the turbine,makes possible both a radial and also a semi-axial impinging onto theturbine wheel. In the radial flow entry cross-section a variablegeometry arrangement is provided with adjustable guide vanes, via whichthe flow entry cross-section can be varied. By adjustment of the guidevanes the gas pressure, as well as the type and manner of the flow ofthe exhaust gas onto the turbine wheel, can be influenced, whereby theperformance of the turbine and the output of the compressor can beadjusted depending upon the requirements and operating condition of theinternal combustion engine.

This type of exhaust gas turbocharger, having variable turbine geometry,is employed also in braking operation of the internal combustion engine.In the braking operation the guide vanes are adjusted into a blocking orchoking position, in which the intake cross-section is significantlyreduced, whereupon an elevated exhaust pressure builds up in the conduitupstream of the turbine, which brings about, that the exhaust gas flowswith increased velocity through the channels between the guide vanes,whereupon the turbine wheel is impinged with a stronger impulse. Thisbrings about an elevated compressor output, so that the fresh orcombustible air reaching the motor is also placed under an elevatedcharge pressure. The cylinder is acted on with increased charge pressureon the inlet side, at the same time the exhaust side is experiencingelevated exhaust gas pressure, which opposes the evacuation orexhausting of the compressed air via the brake value in the exhaust gasconduit. During motor operation the piston in the compression andexhaust stroke must perform compression work against the highoverpressure in the exhaust side, whereby a strong brake effect isachieved.

The desired high brake power can however only be achieved when a desiredpressure distribution exists within the turbine and when the exhaust gasflows through the turbine in the intended manner. It is a problem hereinthat leakages occur on the axial sides of the adjustable guide vanes,which can occur due to construction and manufacturing tolerances,however also due to wear and thermal expansion, and can stronglycompromise the desired pressure relationship within the turbine, whichnegatively influences the motor brake power, and however also negativelyinfluences the motor power in the combustion drive mode. This type ofguide vane leakage results also from gaps inherently required inconstruction to enable movement of the guide vanes of the guide vanering of the variable turbine geometry in the flow entry cross-section.

Similarly, from the publication DE 39 41 399 C1 an exhaust gasturbocharger for an internal combustion engine is known, which isequipped with a twin flow spiral channel with radial and semi-axial flowentry cross-section in the turbine housing, wherein the two flowchannels are separated by a fixed separating wall. Between the radialand the semi-axial flow entry cross-section of the two flow channelsthere is, in the area of the end surface of the separating wallseparating the two flow channels, an axially adjustable slider, which isadjustable between a position blocking the radial inflow cross-sectionand a position blocking the semi-axial inflow cross-section. The sliderassumes the function of a variable geometry turbine part, via which theflow behavior of the flow onto the turbine wheel is to be influenced.Even with this turbocharger design, flow leakage or by-pass cannot beprevented.

The publication DE 35 41 508 C1 discloses an exhaust gas turbochargerwith radial flow entry cross-section towards the turbine wheel, whereinin the flow entry cross-section a guide ring with adjustable guide vanesis provided. Two holder- or mount-rings engaging the guide vanes ontheir end surfaces are connected to each other via multiple screwsdistributed about the circumference. The screws are within spacersleeves, which ensure a minimal separation of the two mounting rings. Anaxial relative movement of the outer support rings relative to the innersupport ring is not possible on the basis of the screw connection, andnamely neither in the direction of a larger separation of the supportrings nor in the direction of a coming together of the support rings.This has only the consequence, that the gap between the axial endsurfaces of the vanes of the guide vane assembly and the two supportrings are arranged with fixed, non-changeable dimensions. Therein acompromise is entered into between having a sufficiently large degree ofmovement for the blades and a sufficiently small gap for avoidance ofby-pass flows. Thermal expansion in the construction components can leadwithin the turbocharger to an enlargement of the gaps and thereby bringabout undesired increase in leakage with correspondingly smallercompressor output.

The publication DE 100 29 640 A1 discloses an exhaust gas turbochargerwith semi-axial and with radial flow entry cross-section to the turbinewheel which are separated by an axially displaceable flow ring. In theradial flow entry cross-section a guide vane ring with adjustable guidevanes and in the semi-axial cross-section a grid with fixed geometry areprovided. If the guide vane ring in the radial cross-section is movedinto the choke or blocking position, then a larger proportion of theexhaust gas flows through the semi-axial cross-section. Aerodynamiceffects can be caused by the displacement of the flow ring in thedirection of the radial ring of guide vanes.

SUMMARY OF THE INVENTION

The present invention is concerned with the task of increasing thedegree of effectiveness of exhaust gas turbochargers having a radialflow entry cross-section and a variable turbine geometry. In particular,during motor braking operation, and in certain cases however also duringcombustion drive operation, the turbine output should be improved.

This problem is inventively solved by the characteristics of claim 1.

According to the design of the new exhaust gas turbocharger, it isprovided that the position of the flow ring in the housing of theturbocharger is variably adjustable. According to the state of the artthis flow ring is always provided as a component fixed with theturbocharger housing, in contrast to which in accordance with new claim1 the flow ring is moveable. By making the flow ring moveable, thepossibility is created to reduce or even completely eliminate the gapdimension which is inherently required in construction to providefreedom of movement to the parts, or is created by wear or thermalexpansion or by other causes. Leakages or flow-by at the end surface ofthe adjustable guide vanes can be substantially or completely excluded,and a desired pressure relationship can be adjusted within the turbine,which imparts a desired gas flow to the turbine wheel. In order to beable to adjust the radial guide vanes, a minimal gap at the axial endsurface of the radial guide vanes is necessary; for adjusting the radialguide vanes the adjustable flow ring can be axially displaced in aposition further distant from the radial ring of guide vanes.Subsequently, for closing of air gaps, the flow ring is advanced untilcontact with the end surface of the radial guide vanes or, as the casemay be, another component of the radial guide grid or to a spacerprovided for this purpose.

The flow ring is designed to be axially displaceable, whereby inparticular guide vane gaps at the radial guide grid can be reduced.Alternatively, or additionally, it can be useful to provide a radialadjustability of the flow ring, which can be accomplished for example byan eccentric displacement of the flow ring and/or by a radial wideningor narrowing of the flow ring.

In the case of an axially displaceable flow ring the displacementmovement is preferably limited by abutments or end stops, which limit inparticular the opening of the guide vane gap of the radial guide grid toa predetermined dimension. This permitted axial movement, which isidentical with the axial play of the flow ring, corresponds preferablyto approximately 0.15 mm to 0.3 mm. This comparatively small dimensionshall ensure that the maximal play of the flow ring is limited to apredetermined dimension or measure, which ensures a functionality of theexhaust gas turbocharger both in the motor brake operation as well as inthe combustion propulsion mode.

The flow ring can, in certain cases, also be mounted floating withoutbeing acted upon by an actuator. In any case, with increasing closure ofthe radial guide grid the static pressure on the guide grid side of theflow ring is strongly reduced, in comparison to which on the oppositelying side, due to the relatively low flow velocities in this area, thepressure remains at a high level. From this pressure differential thereresults a force, which presses the axially moveable flow ring at its endagainst the radial guide grid, whereby the guide grid gaps are reduced.

Axial relief bores can be provided in the flow ring, which extendbetween the axial surfaces of the flow ring, whereby a pressureequalization is made possible and the pressure force acting on the flowring when lying against the the radial guide grid can be trimmed.

In the case of a radial guide grid with adjustable guide vanes these arepreferably mounted, via an axial shaft, preferably on the turbochargerhousing, preferably however also in the displaceable flow ring. In thecase that the guide vanes are mounted double-sided also in the flowring, the flow ring preferably includes recesses for receiving theassociated vane shafts, wherein the depth of the recesses is preferablyadapted to the axial length of the vane shafts, in order to be able toreceive the vane shafts also in the case of a complete closure of theguide vane gap.

It can, in certain cases, also be useful to provide, in certainoperating conditions of the internal combustion engine in motor brakingoperation and/or in the combustion drive mode, a desired measure of gap,with which the flow and pressure relationship within the charger housingin the turbine can, in a predetermined manner, be specifically andpurposefully influenced. Besides this, it can be useful to providesupplemental criteria for the adjustment of the flow ring, for examplein the manner, that the flow entry cross-section for the radial inflowshould not exceed a maximum.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and useful embodiments can be found in the furtherclaims, the description of the figures and the drawings. There is shown:

FIG. 1 a section through a turbine of an exhaust gas turbocharger withvariable turbine geometry and axially adjustable flow ring,

FIG. 2 a representation according to FIG. 1, however with modificationin the area of the radial array of guide vanes,

FIG. 3 a representation corresponding to FIG. 1 or, as the case may be,FIG. 2, however with a further modification in the area of the radialring of guide vanes.

In the embodiments shown in FIGS. 1 through 3 the same components areindicated with the same reference numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

The turbine 1 of an exhaust gas turbocharger for an internal combustionengine shown in FIG. 1, for example for a diesel internal combustionengine or an otto-motor for a utility vehicle or a passenger vehicle,includes a turbine wheel 2 which is powered by exhaust gas underpressure from the internal combustion engine and which drives, via aconnecting shaft, a not shown compressor of the exhaust gasturbocharger, which compressor draws in fresh air and compresses this toan elevated charge pressure, which is conveyed to the cylinder inlets ofthe internal combustion engine. The turbine 1 further includes a flowentry channel 3, which radially encompasses the turbine wheel 2 andincludes a radial flow entry cross-section 3 a going to the turbinewheel 2. In the radial flow entry cross-section 3 a there is a radialring of guide vanes 5 with adjustable guide vanes 6; this radial ring ofguide vanes 5 constitutes a variable turbine geometry.

Depending upon the mode of operation of the internal combustion enginethe variable turbine geometry can be adjusted in its position by anassociated actuation element, whereby the corresponding flow entrycross-section is varied. In the illustrated embodiment it is providedthat in the combusting drive mode the guide vanes 6 of the radial ringof guide vanes 5 are adjusted for example in an open position, in orderto allow the greatest possible mass flow through-put through the turbine1 and to produce a high charger power. For achieving a motor brakepower, in contrast, the radial ring of guide vanes 5 is moved into ablocking position with reduced cross-section by an appropriateadjustment of the guide vanes 6. On the basis of the reduced flow totalcross-section, in comparison to the combustion operation mode, anelevated exhaust gas pressure builds up in the exhaust channel upstreamof the turbine, simultaneously an over-pressurization is produced in theintake stroke. In the motor brake operation brake valves are opened inthe cylinder outlet of the internal combustion engine, the aircompressed in the cylinder must work against the elevated exhaust gaspressure in the exhaust pipe to be pushed out.

In the flow channel 3 of the turbine 1 a flow ring 7 is provided, whichborders the radial flow entry profile or cross-section 3 a. The flowring 7 is axially displaceable in the exhaust gas turbocharger; theaxial displaceability is indicated with the double arrow 8. On theradial inner lying side of the flow ring 7 a sealing ring 11 is seatedin a groove of a housing component, which is associated with the bearinghousing 12, to provide a seal. Preferably the seal ring is held againsta heat shield 13, which is connected fixed with the bearing housing 12.

The housing-fixed heat shield 13 exhibits two steps on the side facingthe flow ring 7, which form abutments for the axially displaceable flowring 7, which exhibits a contour conforming to these steps. In FIG. 1the flow ring 7 is shown in a position lying gap-free against radialring of guide vanes 5; the axial displacement out of this position islimited by the abutments on the housing-fixed component 13, againstwhich the flow ring 7 abuts. The sealing ring 11 prevents leakage bypassflows between the flow ring 7 and the radially inwardly lying,housing-fixed component 13, upon which the flow ring 7 is radiallyseated in the contact position.

In the position shown in FIG. 1 the flow ring 7 lies axially tight orsealingly against the face of the radial ring of guide vanes 5, noradial gap is formed, whereby radial leakage bypass is prevented. In theradial flow entry cross-section 3 a spacer sleeves 14 can also beprovided in addition to the radial ring of guide vanes 5, which limitthe axial displaceability of the flow ring 7 in the direction of theradial ring of guide vanes 5.

The adjustable guide vanes 6 of the radial ring of guide vanes 5 arerotatably mounted in shafts 15 a and 15 b, wherein the two shafts 15 aand 15 b extend out from axially oppositely lying sides of the guidevanes and wherein the first shaft 15 a is received in the housing andthe second shaft 15 b on the other hand is received in the displaceableflow ring 7. The second shaft 15 b is received in a recess in the flowring 7, wherein the depth of the recess corresponds at least to theshaft length, so that in the case of the axially contacting position ofthe flow ring 7 against the radial ring of guide vanes 5 a flush orgap-free axial lying-against is ensured.

The adjustable guide vanes 6 are bordered axially on both sides by coverdiscs 16 and 17, which are received in correspondingly shaped recessesin the receiving housing side component or, as the case may be, in thewall the flow ring 7 facing the guide vanes 6.

The illustrative embodiment shown in FIG. 2 corresponds essentially tothat of FIG. 1, however with the difference that the adjustable guidevanes 6 of the radial ring of guide vanes 5 only exhibit a single shaft15 a on the housing side. This embodiment provides the advantage, thatit becomes possible to dispense with the recesses in the flow ring 7 onthe guide-vane 6 facing side for receiving the corresponding shaftpieces. Also in the embodiment in FIG. 2, two cover discs 16 and 17 areprovided for the two axial sides of the guide vanes 6.

In the illustrative embodiment according to FIG. 3 the guide vane 6 ofthe radial ring of guide vanes 5 essentially exhibits one shaft 15 a onthe housing side and also only one cover disc 16 on the housing side.

Preferably the flow ring 7 and/or the radial ring of guide vanes 5 aredesigned in an aerodynamic manner or, as the case may be, constructedfor flow efficiency, such that the flow ring 7 experiences, due to theinflow over the flow channel 3, a resulting pressure force in the axialdirection of the turbine shaft. The resulting pressure force impingesupon the flow ring 7 preferably in the direction of the radial ring ofguide vanes 5 in the radial flow entry cross-section 3 a, so that theaxial end face gap between the end face side of the radial ring of guidevanes 5 and the flow ring 7 is closed. The aerodynamic design of theradial ring of guide vanes 5 is preferably achieved by the design of theposition of the guide vanes on the radial ring of guide vanes.

It could however also be advantageous that the flow ring is moved in thedirection of an increasing axial gap, in order to prevent over-rotation.

1-10. (canceled)
 11. An exhaust gas turbocharger for an internalcombustion engine, with a turbine adapted for receiving the engineexhaust gas flow, and with a turbine driven compressor for providingintake flow to the internal combustion engine, wherein the turbine (1)has a flow channel (3) with a radial flow entry section (3 a) and afurther flow entry section, wherein a flow ring (7) separates the flowentry cross-section (3 a) and the further flow entry section and bordersthe flow entry cross-section (3 a), wherein an adjustable ring of guidevanes (5) is provided in the radial flow entry cross-section (3 a) forvariably adjusting the flow entry cross-section (3 a), wherein the flowring (7) is axially displaceable in the housing of the exhaust gasturbine (1) between a position contacting the ring of guide vanes (5)and a position exposing a gap between the flow ring (7) and the ring ofguide vanes (5), and wherein axial relief boreholes are provided in theflow ring (7) extending between the axial faces of the flow ring fortrimming of forces acting on the flow ring (7) when lying against theradial ring of guide vanes (5) in such a manner, that as a result of thereduction in static pressure in the ring of guide vanes (5) the flowring (7) experiences a resulting pressure in the direction of the radialring of guide vanes (5).
 12. The exhaust gas turbocharger according toclaim 11, wherein abutments or end stops (18, 19) are provided fixedrelative to the housing for limiting the axial displaceability of theflow ring (7).
 13. The exhaust gas turbocharger according to claim 11,wherein spacer sleeves (14) are provided in the radial flowcross-section (3 a), which determine the minimum axial breadth of theradial flow entry cross-section (3 a).
 14. The exhaust gas turbochargeraccording to claim 11, wherein a seal ring (11) is provided on theradial inner-lying side of the flow ring (7) for sealing against ahousing fixed component (13).
 15. The exhaust gas turbocharger accordingto claim 11, wherein the radial ring of guide vanes (5) includesadjustable guide vanes (6), which include cover discs (16, 17) on atleast one axial end face.
 16. The exhaust gas turbocharger according toclaim 11, wherein adjustable guide vanes (6) of the radial ring of guidevanes (5) are mounted in the turbocharger housing via an axial shaft (15a).
 17. The exhaust gas turbocharger according to claim 11, whereinadjustable guide vanes (6) of the radial ring of guide vanes (5) aremounted in the flow ring (7) via an axial shaft (15 b).